This invention relates to a system and method of detecting and monitoring the treatment of eye disease by determining the presence of visual field defects.
According to recent studies, senile macular degeneration ("SMD") has been determined as one of the leading causes of blindness in the U.S. and Western Europe. The cause of SMD presently is unknown, and the disease may be a result of the aging process. In its mildest form, SMD is a cumulation of changes in the eye which include loss of photoreceptors, accumulation of drusen, pigmentary changes, retinal pigment epithelial cell damage, and other changes. When these changes reach a point in their progression that impairment of central vision occurs, the condition is known as dry or atrophic SMD. This vision impairment typically results in a central visual field defect in the form of a scotoma, i.e., a blind spot. Some scotomas may be detected by kinetic and static tangent screen examination, by threshold automated perimetry and, on occasion, through standard Amsler grid testing.
A small percentage of patients with SMD develop a much more serious form of the disease known as disciform or hemorrhagic SMD. In this advanced form of the disease, new small vessels escape their confinement from the choriod and enter the inner sanctum of the eye under the retina through breaks in Bruch's membrane. In this new subretinal location, the vessels proliferate into a network of vessels that eventually leak protein and bleed, causing localized detachments and irreversible damage to the photoreceptors at the macula. Hemorrhagic SMD is extremely disabling because it severely damages central vision, thus affecting the ability to read and drive. The transition of the disease from the relatively mild atrophic SMD to the more serious hemorrhagic SMD takes place in a relatively short three to four week period. After this three to four week period, hemorrhaging of the subretinal new vessels can occur at any time and produce disastrous permanent damage to central vision.
Known methods of determining this new vessel growth include tangent screen examination and threshold automated perimetry. If the scotomas indicating the presence of atrophic SMD have increased in size from previous tests, then it is an indication that new vessel growth may be occurring. Attempts to use standard Amsler grid testing as another method generally have failed because it is a supra-threshold test lacking sufficient sensitivity to accurately and consistently detect the presence of relative scotomas in the central visual field.
Fortunately, there are treatments for the disease during the critical three to four week period of new vessel growth to prevent advancement to the severe stage of hemorrhagic SMD. One of the more recent effective treatments has been photocoagulation treatment, in which a laser beam is used to destroy and halt the growth of the new vessels under the retina. Once the vessels are destroyed, protein and blood outflow usually stop, and the potential for further vessel growth is minimized.
Unfortunately, however, the existing methods for detecting new vessel growth, prior to advancement of the disease to hemorrhagic SMD, are time consuming, relatively expensive, or unreliable. Thus, while patients who have developed atrophic SMD should be tested frequently to identify the presence or absence of new vessel growth, many are reluctant or financially unable to undergo testing on such a frequent basis. Many patients often are confronted with the dilemma of balancing the needs of their time and finances with the horrible possibility that they may permanently lose their central vision if not tested frequently enough to detect the new vessel growth. Moreover, there is the statistical consideration that only a small percentage of those with atrophic SMD, approximately five to fifteen percent, go on to develop hemorrhagic SMD.
Accordingly, there has existed a definite need for an efficient and reliable system and method of detecting and monitoring atrophic SMD before the disease advances to the severe stage of hemorrhagic SMD. There also generally has existed a need for a system and method of detecting visual field defects that is inexpensive and not time consuming. The present invention satisfies these needs and provides further related advantages.